Freshwater Species of the week

Freshwater ecosystems are home to an incredible diversity of species. Rivers, lakes, swamps, peatlands and all the other freshwater wetlands harbour more than 10% of the world's species. Each week, we will profile one of the most extraordinary.

The flatworm, Crenobia alpina, is not your typical freshwater star species. With two primitive eyespots giving them a charismatic look, this species can grow up to 15mm in length (take a look at them moving here). This harmless flatworm is a predator found most frequently in cold and clear mountain streams. Their preference for cold waters comes with a price in a climate-changing world – a 40-year study shows that this species (as well as other invertebrates) has vanished from Llyn Brianne and much of Wales when the temperature of the streams rose. As the professor of ecology at Cardiff University’s school of biosciences, Steve Ormerod says, “the loss of freshwater organisms is a hidden tragedy, and it’s amazing how much is left to discover”.

The striking Painted terrapin, Batagur borneoensis, is a freshwater turtle native to Brunei Darussalam, Indonesia, Malaysia, and Thailand. They present plain grey skin and shell for most of the time, letting their beautiful colours only pop during the mating season from January to June. The males are the ones to go through the transformation and “paint” themselves – their carapace lightens in colour to showcase striking black markings, and their heads turn to pure white with a bright red strip between their eyes. The female terrapins nest in beaches, but instead of the new-borns (a.k.a hatchlings) heading to the open ocean like their sea-going “cousins”, they make their way towards fresh and brackish waters. After reaching their mating age, pregnant Painted terrapins return to the same beach where they once hatched to lay their own eggs - the circle of life! This predictable behaviour, however, is one of the reasons this species is listed as Critically Endangered on the IUCN Red List of Threatened Species – it makes them vulnerable to habitat destruction and poachers who steal the eggs to eat or sell. Learn more about this incredible species and WWF conservation efforts with this great read.

Endemic to Lake Malawi in East Africa, the Chambo, Oreochromis karongae, likes to swim around in loose shoals. Like other fishes of the Oreochromis genus, they present a curious form of parental care called maternal mouthbrooding. During spawning, soon after the male has fertilized the eggs, the mother puts them in her mouth until they hatch – a fascinating strategy to protect their offspring. The Chambo is also very important for local subsistence and commerce, being the most valuable food fish in Malawi. For this reason, they are threatened by overfishing. In the 1990s, the populations of the Chambo collapsed, with a 70% decline within ten years – unsurprisingly ending up listed as Critically Endangered by the IUCN Red List of Threatened Species.

The Spoon-billed sandpiper, Calidris pygmaea, is a petite wading bird with a unique spatula-shaped bill. With their heads down in shallow and wet meadows, they move their bills side to side to look for food, also using it sometimes as a shovel. This migratory bird has a very specialised breeding habitat found in north-eastern Russia – lagoon spits where they can nest among crowberry plants, dwarf birch, and willow sedges with adjacent estuary or mudflats. During winter, they migrate down the Pacific coast to Southeast Asia – relying heavily on intertidal areas of the Yellow Sea along the way. Unfortunately, their stopover habitats, as well as their breeding and wintering grounds, are being degraded, resulting in the Spoon-billed sandpiper being one of the world’s most endangered birds. They are listed as Critically Endangered by the IUCN Red List of Threatened Species. As a response, the Spoon-billed sandpiper is one of the priority species of our Asian Flyways initiative, which aims to restore and protect an international network of wetlands used by this and other migratory birds populations.

Did you know that jellyfish also exist in freshwater systems? Native to the Yangtze River valley in China, the Freshwater jellyfish, Craspedacusta sowerbii, prefers to live in still or slow-moving water bodies such as ponds, reservoirs, quarries, and lakes. Similarly to other jellyfish, they have a complex life cycle that generally includes 5 moments: microscopic podocytes (dormant "resting bodies"), two different larvae phases, polyp phase, and the most recognizable (but least common in the environment) – the hydromedusa (right picture). As opportunistic predators, the Freshwater jellyfish feeds on small organisms that come within its reach, capturing their prey with the (in)famous stingers. But there’s no need to worry next time you take a dip in a lake - the stinging cells are so small that they usually don’t hurt vertebrates.

This week we celebrate the exquisite and outstanding Lesser flamingo, Phoenicopterus minor. This species is “lesser” only in the sense that it is the smallest of the six species of the flamingo family. They have the biggest population of all flamingos, with two to three million individuals. They are also tolerant to extreme environments – their habitat is hostile for many animals and plants due to high temperatures, salinity, and alkalinity, but the Lesser flamingos are superbly adapted. Living around lagoons or lakes of Africa and India, they walk through shallow waters with their thin, pink legs as they feed - bending their necks downward to filter their food. It is thanks to their diet - rich in carotenoid pigments - that their feathers become remarkably pinkish. The bright pink colouration may function as a signal of parental capability, attracting mating partners – as parents take turns in brooding, one of them needs to look for food efficiently. The Lesser flamingo also shines with their spectacular courtship dance: groups of more than 1000 birds march together with a straight-up posture like soldiers, moving their heads and necks synchronously. These extraordinarily social birds also synchronize other activities such as brooding, to “crowd-protect” their offspring. A recent study even suggests that they form lifelong friendships – making it impossible not to fall for the flamboyant flamingo.

The Waterwheel plant, Aldrovanda vesiculosa, might seem harmless with its tiny and delicate appearance while free-floating its “rootless-self” in peat-bog pools, lakes, and river deltas. Especially for an unsuspecting small aquatic invertebrate, who gets unwittingly too close to the Waterwheel and…SNAP! It is trapped in their prey-catching leaves. This remarkable and rare carnivorous aquatic plant has a snap-trap system that can be set off inadvertently by their game - the prey stimulates, mechanically, trigger hairs found in the central region of the trap leaves, prompting the two trap lobes to rapidly (as short as ten milliseconds!) move toward each other. Sadly, this unique species is listed as Endangered by the IUCN Red List of Threatened Species, known in only 50 isolated populations across the globe. The Waterwheel plant faces many threats, including eutrophication and degradation of its wetland habitat, driven by unsustainable agriculture and development.

To celebrate Dolphin Day (April 14th), we present to you the charmingIrrawaddy river dolphin, Orcaella brevirostris. With a rounded head and no beak, the three subpopulations of this distinctive dolphin can be found swimming along three rivers in South and Southeast Asia - Ayeyarwady River (Myanmar), Mahakam (Indonesia) and Mekong (Cambodia). Recent estimates indicate that there are around 79 individuals left on the Ayeyarwady, indicating this is a species right on the edge. Nonetheless, less than 300 freshwater Irrawaddy dolphins still live, including in Cambodia and Indonesia. Although they are not directly exploited, these river dolphins suffer many threats, including entanglement in gill nets and illegal fishing activities such as electrofishing - which unsustainably removes their food source. Nevertheless, fishing activities can be done in harmony with river dolphins. In the Ayeyarwady river, the local fisherfolk use a traditional fishing method that portrays a unique relationship with the dolphins, called “Cooperative fishing”. The fishermen “call” the dolphins by tapping a stick repeatedly on the side of the boat. If the dolphins are up to fishing, they chase shoals of fish towards the waiting nets and signalize the location of the prey. Once the fishermen cast their nets, the dolphins snatch the escaping fish. As this extraordinary interaction can be seen only in a few places around the world, many initiatives – such as ourRiver Dolphin Rivers - work on the conservation of both the Irrawaddy dolphin and the fishermen’s way of life.

The Surinam toad, Pipa pipa, is a fully aquatic amphibian known for its unusual appearance and fascinating – some might argue horrifying - parental care adaptations. You can find this species mostly in the slow-flowing waters of the Amazon Basin in South America, generally hiding under submerged leaf-litter - with their extremely flattened body and triangular-shaped head, they blend in for looking like a mottled brown leaf. This species also exhibits a unique courtship behaviour: after attracting a mate by making clicking sounds, the male toad mounts onto the back of the larger female and embraces her around the waist - if she is receptive, their mating act starts, and the pair displays some aquatic somersaults that can last for more than 12 hours. With the help of the male, the fertilized eggs are rolled up onto the back of the now upside-down female – the eggs sink into the puffy and swollen skin and are almost completely enveloped by it. The pregnant toad carries the developing offspring for three to five months until the “toadlets” are ready to punch their way out of their mother’s skin pockets, in a bizarre scene that can make many people shiver.

The Net-spinning caddis, Hydropsyche siltalai, is a species of Caddisfly; insects that are aquatic as larvae. They spend up to a year in lakes and rivers around the world before emerging as adults - and graduated engineers. One might think that larvae can’t be up to much, but the Net-spinning caddis larvae are quite busy building their retreat - a fascinating dreamcatcher-like silk structure. The larvae produce silk threads and weave it into fine-meshed nets that filter food particles from the water column while sheltering them. Recently, scientists found that these silk structures might influence local hydraulics – they can reduce flow downstream by 95% and upstream by 17%, besides altering turbulence (for more information, check the scientific paper). Even though the impressive caddis larvae seem to be well prepared to face the world and reach adulthood, recent research showed that they are in sharp decline - vulnerable to changes in climate.

World Water Day was on March 22nd, and to celebrate our most precious resource, we introduce you to the northernmost freshwater fish in the world: the beautiful Arctic char, Salvelinus alpinus. These circumpolar fish species inhabit cold and clean waters around the North Pole. Numerous local freshwater populations of Arctic char exist in all Arctic states, plus a smaller number of sea-run populations - where fish can grow up to 10kg in weight. The Arctic char suffers from increasing temperatures due to climate change, especially the more southern populations in the Alpine regions, which can be at risk of extinction - water temperature and quality are significant factors in the survival of their sensitive eggs. According to the first report on The State of the Arctic Freshwater Biodiversity (2019), climate warming increasingly threatens freshwater biodiversity in arctic lakes, rivers, and wetlands. The report also suggests that the Arctic char – as well as other cold-water species endemic to the Arctic – are likely to suffer regional losses, or even local extinctions as a result (find out more with this great article). Similarly, the 2019 report of the Intergovernmental Panel on Climate Change (IPCC) states that changes in the cryosphere will alter freshwater communities - range shrinkage and extinction of some species can cause regional biodiversity to decrease. WWF Finland has been involved in a conservation project to strengthen the population of Critically Endangered Lake Saimaa Arctic char. Also good news exists: exploitation of the northern Arctic char population in Finland has decreased at the same time with improved protection, leading to improved conservation status in the Red Book of Species for Finland – bending the curve in freshwater species does exist!

In the rivers and streams of Tasmania lives the world’s largest freshwater invertebrate – the endemic Giant freshwater crayfish, Astacopsis gouldi. The IUCN Red List of Threatened Species list this species as Endangered, mainly as a result of years of past overfishing, illegal fishing, and habitat loss and degradation. Capable of reaching 6kg in weight, they have been harvested as a food source at a local and national level. The effects of fishing pressure are aggravated by their biological characteristics - this menacing-looking giant is actually very easy to catch, besides being slow-growing with low breeding potential. This species has received attention as a species of conservation concern - in the 90s, the Australian and Tasmanian governments added the Giant freshwater crayfish to their environmental legislation, and, recently, the critical habitat has been redefined.

A long time ago, a young warrior called Naiá, from a Brazilian Amazonian tribe – “Tupi-guarani”– would dream about the day she would meet with Jaci, the moon. According to the legend, Jaci was a goddess who every night would kiss the most beautiful women of the tribe, and before hiding behind the mountains, she would pick her favourite to transform the woman into a star. Every night, Naiá would walk around the hills searching for Jaci. One day, after seeing the reflection of Jaci on a lake, she threw herself inside the lake and drowned. The moon compassionately decided to reward Naiá for her sacrifice, transforming her into a star of the waters – the Victoria water lily, whose white flower only opens at night and changes to pink when the sun rises. The myth of the Victoria water lily above is a fragment of the memory of WWF's Paula Martinelli, who remembers hearing this story growing up in Brazil. The Victoria water lily, Victoria amazonica, is native to the Amazon biome and the symbol of the Amazon state of Brazil. The legend of the Victoria water lily has some truth to it – the white flowers only bloom at night, its colour changing to pink or ruby red after spending the evening exuding a strong odour to attract beetles to pollinate them. The flower closes its petals in the morning, hopefully trapping the beetles and releasing pollen on them. They open again in the following evening, releasing the beetles to transport their pollen to other flowers – they now have different colours and are scentless, being less attractive to the beetles. This fascinating adaptation avoids fertilization by its own pollen, increasing the genetic variability of the world’s largest water lily.

To celebrate World Wildlife Day (tomorrow on March 3rd), this week we present to you the majestic Beluga sturgeon! Even though there is still a debate on which is the largest freshwater fish in the world, the Beluga sturgeon, Huso huso, is undoubtedly the largest migrating freshwater fish – with a record of 1,571 kg and 7.2 m, this female was caught in 1827 in the Volga estuary. But this is history - nowadays, you can seldom observe a length above 2m. This species has been recorded swimming in the basins of the Caspian, Black, Azov, and Adriatic Seas. The migration of the Beluga sturgeon was predictable, and as a huge fish, they were an easy target, providing abundant food for many people. Its current native wild distribution is restricted to the Black Sea (Danube and Rioni) and the Caspian Sea (Ural). It does occur in the Azov Sea and Volga River, but as stocked fish. Due to historically severe overfishing and poaching in estuaries and rivers, the Beluga sturgeon is listed as Critically Endangered (CE) by the IUCN Red List of Threatened Species. This species is wanted for its meat and caviar - one of the most valuable products on the food market. Their caviar is considered top class caviar and is among the most expensive – you can buy 30g in London at the modest price of €420, which adds up to a price of €14.000 per kg. The beluga sturgeons’ eggs can only be legally obtained from aquaculture. Unfortunately, illegal wild caviar is still in demand on the black market by customers who consider "wild" as the "real" thing. IUCN also states that sturgeons are more critically endangered than any other group of species – 23 of all 27 known species are considered to be threatened with extinction. The mighty Beluga sturgeon can live for over 100 years, spending several years in the sea and migrating longer distances than any other sturgeon – more than 1000km. Because of their particular long life cycle, the recovery of its heavily depleted stocks will need several decades. But they can still be saved. WWF is working together with communities, civil society, companies, scientists, law enforcement authorities and governments across the world to rebuild their population. For example, our Sturgeon initiative is tackling the illegal caviar trade and enhancing the health of river systems. And, last year, WWF helped to save a Beluga in the Danube.

The Giant freshwater stingray, Urogymnus polylepis, is one of the largest and heaviest freshwater fishes in the world. With the ability to gain more than 600kg and 2m disc width, this freshwater giant mostly swims the large rivers of south and southeast Asia ( find out more about the beautiful Giant stingray and other giants of the Mekong river in this report). The IUCN Red List of Threatened Species lists the Giant freshwater stingray as Endangered, mainly due to fisheries and habitat degradation. The development of dams is also one of the drivers for their – and other freshwater megafauna species – population declines. Among WWF’s conservation efforts is our Resilient Asian Deltas (RAD) Initiative, whose ambition is to secure healthy and functioning river systems from source to delta through unprecedented political and financial investment in ‘building with nature’. To address the crisis facing freshwater biodiversity like the Giant freshwater stingray, WWF has just published an Emergency Recovery Plan - together with scientists from across the world - as a call to action to the world’s decision makers to value, protect and restore freshwater habitats before it’s too late.

The Grey Crowned crane, Balearica regulorum, calls attention for its beautiful colours and a majestic golden plumage on their head unfolding like a crown. They are also known for displaying playful behaviours such as dancing. Mainly a form of socialization and pair formation, other species of cranes are also famous for their dance moves. You can find the Grey Crowned crane “performing” in the eastern and southern regions of Africa, where they are also a culturally important species – considered icons of Africa’s wetlands and savannahs, besides being the national bird of Uganda. However, it’s not all glamour for the Grey Crowned crane. Listed as Endangered by the IUCN list of threatened species, they are threatened primarily by illegal trade, disturbance, and habitat loss. The Global Wetland Outlook 2018 states that up to 87% of wetlands have been lost since 1700. The Grey Crowned crane and the other 14 living species of cranes need wetlands as stepping stone corridors – where they can find a safe harbour to sleep, rest, nesting, and rearing the young. As cranes are among the most threatened bird families in the world, WWF has joined the International Year of Crane 2020, announced by the International Crane Foundation and the Crane Working Group of Eurasia. The Amur River basin is the flyway and breeding grounds of no less than six species of cranes, and WWF will be working with partners in the region to strengthen the conservation of both wetlands and the majestic cranes.

The Rainbow mussel, Villosa iris, is a fascinating freshwater species not only for its beautiful inside shell, which is iridescent – they are also the master of disguise! “Hidden” in the North American rivers and streams, this tiny mussel uses mimicry to increase its odds of success: the mussel lures fishes by looking and moving like a crayfish, which is, in reality, a few flaps of fleshy skin coming out of its shell. Once the fish is close enough to take a bite of the “crayfish”, the Rainbow mussel releases a cloud of tens of thousands of parasitic spawn! Aiming for a safe place to transition into juvenile mussels, the mussel larvae latch to the fish’s gills, fins, and skin. Their new “home” (and “ride”) also provide for their food – they feed on the minuscule amounts of nutrients from their host. Most of the time, however, the fooled host-fish is not harmed by this interaction.

The Golden Mahseer, Tor putitora, is one of the world’s most iconic freshwater fish – highly prized by anglers, it is viewed as a God fish by local communities in some parts of South Asia, such as India and Bhutan. But its numbers are declining across South and South East Asia due to a range of threats from dam blocking its migratory routes to pollution and unsustainable fishing. It is now classified as Endangered on the IUCN Red List of threatened species. Local communities in India have revered fish species as symbols of divine power, offering them protection and building temple sanctuaries along the river banks, the first established nearly 1200 years ago. The Golden Mahseer benefits from this protection in several stretches of the river Ganges associated with these temples, where fishing is not allowed, and local communities, pilgrims, and temple authorities help to monitor and protect the mahseer population. The Mahseer also has cultural, religious and economic significance in Bhutan, where it is known as the Tiger of the River (you can find out more in this great documentary on the “Tiger of the River” produced by WWF Bhutan). In 2015, as a response to the pressures on Bhutan’s river systems, the Fisheries Conservation Foundation, WWF Bhutan, and the Ministry of Agriculture and Forests started a partnership to assess the migration pattern of the God fish using radio telemetry technology. This year, the 2nd International Mahseer Conference is being held in Thailand from 11th to 15th February, where researchers and conservationists - including WWF - will share knowledge, collaborate and promote the conservation of the species.

The Yangtze Finless porpoise, Neophocaena asiaeorientalis asiaeorientalis, as the name suggests, lives in the Yangtze River and is the world’s only freshwater porpoise – and one of only five surviving species of freshwater cetacean. Unfortunately, there are only an estimated 1,012 finless porpoises left in China’s greatest river and they are listed as Critically Endangered on the IUCN red list of threatened species due to a host of threats, including water pollution, overfishing, boat traffic, sand mining, and river fragmentation. Many finless porpoises have also been killed after becoming accidentally entangled in gill nets – something which contributed to the extinction of the Yangtze freshwater dolphin, the Baiji (Lipotes vexillifer). But there is still hope for the Yangtze finless porpoise. Led by the Chinese government, conservation efforts – involving WWF, partners and local communities – have helped to drastically slow the annual decline in the finless porpoise population, including relocating animals to safer habitats away from the river’s mainstem to create new breeding populations. Huge amounts of work still need to be done to secure the survival of the species and WWF will continue to be at the forefront through its global River Dolphin Rivers initiative. This initiative is working on the development of smart river pingers in an effort to prevent future entanglement in gillnets. For many years, the finless porpoise had little to smile about but thanks to the combined efforts of the government, communities and conservationists, there is now a chance that the species can turn the corner and that its population will finally start to increase.

The Hellbender salamander, Cryptobranchus alleganiensis, a.k.a. giant salamander, is, non-surprisingly, the largest salamander in North America – and the third-largest in the world. But these amphibian giants are fascinating not only for their size: they have lungs, but they mostly breathe through their wrinkly skin; they can swim, but usually walk underwater through their sturdy limbs. With tiny eyes on the top of their heads and light-sensitive cells all over their bodies, especially on their tails, they can keep their (giant) selves completely hidden from large fish under rocks and use their keen sense of smell to hunt crayfish. Besides playing this important role in their ecosystem, they are also bioindicators of stream quality, as they have a low tolerance for poor water quality. It is not a good sign for the North American rivers that their populations are considered Near Threatened by the International Union for Nature Conservation (IUCN), mainly due to the worsening condition of their freshwater habitats. Find out more about this species in this cool video by David Herasmtschuk.

The matamata turtle, Chelus fimbriata, is one of the world’s largest freshwater turtles – and undeniably one of the weirdest too. Found in the Amazon and Orinoco basins, their unmistakable appearance is the combination of a leaf-shaped head, a long pointy snout, a rough tuberculate flat shell, and an elongated, thick neck with protuberances. The bizarre look is the result of a unique adaptation for feeding and blending in - they are incredibly specialized feeders that wait for dinner to come to them. When unknowing fish approach them to see if the protuberances on their neck are edible, they quickly stretch their neck out and open their mouth to create a vacuum that swallows their prey whole.

For the first week we are highlighting the European eel, Anguilla anguilla. There can be few species more mysterious than the European eel, Anguilla Anguilla. A species that breeds just once in its lifetime and must travel thousands of kilometres to do so. European eels, like other Anguillid eels exhibit a number of life stages: they start their lives in the ocean as leptocephalus (larvae) which float back to estuaries where they turn into glass eels, and then elvers before travelling upstream into our rivers where they turn into yellow eels. The final stage of an European eel’s life is as a silver eel; silver eels are able to migrate thousands of kilometres to the Sargasso sea to spawn. No one has witnessed their spawning and so the spawning location remains a hypothesis. European eels are a Critically Endangered species, threatened by dams and infrastructure, habitat destruction and illegal trafficking. Find out more about this enigmatic and mysterious freshwater species in this great article.If you’d like to find out about other Anguillid species, check out this blog from Kathy Hughes, our very own Freshwater Habitats and Species ACAI lead. Kathy like’s eels so much she takes holidays especially to swim with them.

Questions?

If you want more information on our Freshwater Species of the Week, or even suggest an increadible species, please contact Paula Martinelli (pmartinelli@wwfint.org).